Hail — Jefferson, Montana

2019-07-12 · near Whitehall, Jefferson, Montana

Event narrative

Trained spotter reported 1.5 inch hail in Whitehall.

Wider weather episode

A of broad low pressure area over the Pacific Northwest exerted an influence on Montana's weather for much of the weekend. This resulted in a persistent unstable southwest flow over the region, which pumped in mid and upper level moisture along with passing disturbances embedded within the flow. In the upper levels, a jet stream was situated in a favorable position to produce upper level divergence. Meanwhile, a low level easterly flow was present for a significant period of time, which further increased moisture levels and wind shear. During the peak of this event, precipitable water values approached the one inch mark, effective wind shear values were as high as 50kts, and mid-level lapse rates soared to 7.5 to 8 degree C per Kilometer. The combination of these conditions provided an environment primed for a weekend of severe thunderstorms for much of the region.

View location on OpenStreetMap → (45.8700, -112.1000)

Source: NOAA Storm Events Database, event_id 840774. Narrative written by the NWS forecast office that issued the report.